AMBROX.RTM. (registered tradename of Firmenich SA, Geneva, Switzerland) or 3a,6,6,9a-tetramethylperhydronaphto[2,1-b]furan is one of the ingredients of choice in a great variety of perfuming compositions. Its characteristic odor of ambergris possesses a special power of diffusiveness which has remained so far unmatched. Since its discovery [see Helv. Chim. Acta 33, 1251 (1950)] numerous syntheses for its preparation have been proposed by different research groups. These utilise the oxidative degradation technic on diterpenes such as sclareol or manool, or use ambreine as starting material [G. Ohloff in Fragrance Chemistry, Ed. Ernst T. Theimer, p. 545, Academic Press (1982)].
Among the compounds having a structure analogous to that of AMBROX, the following oxygenated decalinic aldehydes have been described in the prior art ##STR5## wherein the dotted lines represent an additional double bond [see British Pat. No. 701,911 and West-German Pat. No. 1,019,031 and Parfumerie and Kosmetik 54, 335 (1973)]. Very appreciated for their ambergris fragrance, these compounds represent not only useful perfuming ingredients but also they have a utility as intermediates for the preparation of AMBROX.
In effect, the said aldehydes together with the corresponding acids can be reduced to their corresponding carbinols, e.g. by treatment with LiAlH.sub.4, which carbinols through acidic cyclisation give the desired AMBROX according to the following reaction pathway: ##STR6##
The oxygenated decaline derivatives of formula (I) have been obtained in the past by processes [see above mentioned references] which in actual experience are uneconomical either because they do not enable the preparation of the desired end-product in useful yields or because they use polluting reactants or non easily available products.